1. Field of the Invention
This invention relates generally to the field of power transmission in a driveline for an automotive vehicle. More particularly, it pertains to a method of shifting multi-speed axles to drivably connect relatively rotating shafts in the driveline of a motor vehicle.
2. Description of the Prior Art
To drivably connect relatively rotating shafts, a mechanical synchronizer is commonly provided to synchronize the rotational speed of the shafts, an example of which is provided in U.S. Pat. No. 4,375,172. The device of the '072 patent is a relatively effective mechanism, but is produced at high cost and not able to engage over a wide speed variation.
It would be desirable to provide a non-blocked engagement device for engaging relatively rotating shafts.
Also, multi-speed axles are commonly used on vehicle drivelines to incorporate different final drive ratios. This allows, for example, a highway gear, for fuel economy, and a towing gear, for maximum vehicle pulling power. Multi-speed axles are typically manually operated and are found on heavy trucks, which have manual transmissions. The use of a manually operated multi-speed axle generally requires a relatively skilled driver with the ability to properly manipulate the accelerator pedal during shifts to synchronize engine speed to axle speed, which has a direct impact on shift smoothness and axle durability.
Currently, the disadvantages of using multi-speed axles, i.e. skilled drivers and manual transmissions, outweigh the advantages, i.e. improved fuel economy with maximum pulling power. With the increased consumer use of light trucks and sport utility vehicles, however, improved fuel economy combined with maximum pulling power and the use of an automatic transmission are very desirable. The need, therefore, is to develop a multi-speed axle capable of providing improved fuel economy and maximum pulling power for use by a typical driver with an automatic transmission.